Aircraft electrical power typically comes from different sources depending on whether the aircraft is on the ground, preparing for takeoff, or in flight. For instance, when the aircraft is on the ground and parked at a terminal, electrical power is usually provided via a removable power cable that connects the aircraft to a ground power source. This ground power source typically provides the aircraft with AC power that is subsequently converted to DC power by rectifying equipment located on the aircraft. As the aircraft prepares for takeoff, the ground power source is unplugged and an auxiliary power unit (APU) is switched on by a contactor to provide the aircraft electrical system with power. The APU is preferably a self-contained generator that runs off a combustion or gas turbine engine and is designed to provide the aircraft with electrical power during periods when the main aircraft engines are turned off. Generating power with the APU, as opposed to an engine generator (which requires operation of an aircraft main engine), saves fuel and wear-and-tear on the engine. Once the main engines are turned on, power generation transfers from the APU to one or more engine generators which provide the aircraft with electrical power throughout the remainder of the flight. After the aircraft has landed and parked, it may be desirable to turn off the aircraft electrical system by switching contactor to an ‘off’ state.
As is known by those skilled in the art, some contactors operate on a ‘break-before-make’ principal. In this arrangement, when the contactor switches between the various power sources there is a temporary interruption in the electrical power supplied to the aircraft electrical system. This temporary interruption, which usually only lasts a few milliseconds to several hundred milliseconds, can cause some of the aircraft's electronics to turn off, reset, and/or erase information that has already been programmed, to name but a few ramifications.